1. Field of the Invention
The present invention relates generally to methods, systems and compositions for making and using a porous bioresorbable dressing comprising bioresorbable microspheres for use in conjunction with reduced pressure wound therapy.
2. Description of Related Art
Wound healing may be broadly split into three overlapping basic phases: inflammation, proliferation, and maturation. The inflammatory phase is characterized by hemostasis and inflammation. The next phase consists mainly of epithelialization, angiogenesis, granulation tissue formation, and collagen deposition. The final phase includes maturation and remodeling. The complexity of the three step wound healing process is augmented by the influence of local factors such as ischemia, edema, and infection, and systemic factors such as diabetes, age, hypothyroidism, malnutrition, and obesity. The rate limiting step of wound healing, however, is often angiogenesis. Wound angiogenesis is marked by endothelial cell migration and capillary formation where the sprouting of capillaries into the wound bed is critical to support the regenerating tissue. The granulation phase and tissue deposition require nutrients supplied by the capillaries. Impairments in wound angiogenesis therefore may lead to chronic problem wounds.
Expression of the angiogenic phenotype is a complex process that requires a number of cellular and molecular events to occur in sequential steps. Some of these activities include endothelial cell proliferation, degradation of surrounding basement membrane, migration of endothelial cells through the connective tissue stroma, formation of tube-like structures, and maturation of endothelial-lined tubes into new blood vessels. Angiogenesis is controlled by positive and negative regulators. In addition to endothelial cells, cells associated with tissue repair, such as platelets, monocytes, and macrophages, release angiogenic growth factors, such as vascular endothelial growth factor (VEGF) into injured sites that initiate angiogenesis.
There are currently several methods used to augment wound healing, including irrigating the wound to remove of toxins and bacteria, local and systemic antibiotics and anesthetics, and local application of growth factors. One of the most successful ways to promote wound healing in soft tissue wounds that are slow to heal or non-healing is reduced pressure therapy. Reduced pressure therapy generally refers to application of a pressure less than the ambient pressure at the wound site, where the magnitude and time period of the reduced pressure treatment is sufficient to promote healing or tissue growth. Examples of devices used to apply reduced pressure include those popularized by Kinetic Concepts, Inc. of San Antonio, Tex., by its commercially available VACUUM ASSISTED CLOSURE® or V.A.C.® product line. The reduced pressure induced healing process has been described in U.S. Pat. Nos. 5,636,643 and 5,645,081, the disclosures of which are incorporated fully by reference.
The reduced pressure serves to promote the migration of epithelial tissue and subcutaneous tissue from the healthy tissue towards the wound site. Typical reduced pressure therapy includes application of reduced pressure to a wound site through a dressing that serves as a manifold to distribute the reduced pressure. The dressing is sized to fit the existing wound, placed in contact with the wound, and then periodically replaced with smaller pieces of dressing as the wound begins to heal and becomes smaller. While use of reduced pressure therapy with the dressing has been highly successful, there still exists various difficulties with this process. For example, it may be difficult to obtain a dressing of a proper width, length or depth to properly fit the wound. Further, as the dressing is removed it may also remove healthy tissue, thereby causing further trauma to the wound site.
It has been proposed to use biodegradable materials to make the dressing, thereby resulting in a dressing that need not be removed from the wound site. With many of these dressings, however, the biodegradable polymer is formed in advance into a particular shape. Individual wounds, however, are of inconsistent shapes and sizes.
A need exists, therefore, for a dressing that be easily manufactured and configured to a shape and size to fit the individual patient's wound. A need also exists for a dressing that need not be removed from the wound site. Further, a need exists for a dressing that contains pores such that the dressing can promote healing and healthy tissue growth at the wound site by inducing granulation tissue formation.
All references cited herein are incorporated by reference to the maximum extent allowable by law. To the extent a reference may not be fully incorporated herein, it is incorporated by reference for background purposes and indicative of the knowledge of one of ordinary skill in the art.